EBS gives you persistent, high-performance, high-availability block-level storage which you can attach to a running instance of EC2. You can format it and mount it as a file system, or you can access the raw storage directly. You can, of course, host a database on an EBS volume.

While S3 is great for storage, EBS is more flexible with its uses. EBS is used in tandem with EC2 instances. But normally, when an EC2 instance goes away, its storage disappears, too. EBS is, as Amazon says, persistent. It sticks around.

The costs are similar to other Amazon Web Services, which charge by usage. Storage is 10 cents a GB per month. I/O requests are 10 cents per million. There’s a AWS calculator to help you figure out your own costs.